Dolastatin 15 derivatives

ABSTRACT

Compounds of the present invention include cell growth inhibitors which are peptides of Formula I,
 
A-B-D-E-F-(G) r -(K) s -L  (I),
 
and acid salts thereof, wherein A, B, D, E, F, G and K are α-amino acid residues, and s and r are each, independently, 0 or 1. L is a monovalent radical, such as, for example, an amino group, an N-substituted amino group, a β-hydroxylamino group, a hydrazido group, an alkoxy group, a thioalkoxy group, an aminoxy group, or an oximato group. The present invention also includes a method for treating cancer in a mammal, such as a human, comprising administering to the mammal an effective amount of a compound of Formula I in a pharmaceutically acceptable composition.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/406,512 filed Apr. 18, 2006, which is a continuation of U.S.application Ser. No. 10/255,118 filed Sep. 25, 2002, which is acontinuation of U.S. application Ser. No. 09/618,694 filed Jul. 18,2000, which is a continuation of U.S. application Ser. No. 08/896,394filed Jul. 18, 1997, the entire contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

A number of short peptides with significant activity as inhibitors ofcell growth have been isolated from the Indian Ocean sea hare Dolabellaauricularia (Bai et al., Biochem. Pharmacology, 40: 1859-1864 (1990);Beckwith et al., J. Natl. Cancer Inst., 85: 483-488 (1993) andreferences cited therein). These include Dolastatins 1-10 (U.S. Pat. No.4,816,444, issued to Pettit et al.) and Dolastatin-15 (European PatentApplication No. 398558). Dolastatin 15, for example, markedly inhibitsthe growth of the National Cancer Institute's P388 lymphocytic leukemia(PS system) cell line, a strong predictor of efficacy against varioustypes of human malignancies.

The exceedingly small amounts of the various Dolastin peptides presentin Dolabella auricularia (about 1 mg each per 100 kg sea hare) and theconsequent difficulties in purifying amounts sufficient for evaluationand use, have motivated efforts toward the synthesis of these compounds(Roux et al., Tetrahedron 50: 5345-5360 (1994); Shioiri et al.,Tetrahedron 49: 1913-24 (1993); Patino et al., Tetrahedron 48: 4115-4122(1992) and references cited therein). Synthetic Dolastatin 15, however,suffers from drawbacks which include poor solubility in aqueous systemsand the need for expensive starting materials for its synthesis. These,in turn, have led to the synthesis and evaluation of structurallymodified Dolastatin 15 derivatives [cf.: Biorg. Med. Chem. Lett. 4:1947-50 (1994); WO 93 03054; JP-A-06234790; WO 93 23424].

However, there is a need for synthetic compounds with the biologicalactivity of Dolastatin 15 which have useful aqueous solubility and canbe produced efficiently and economically.

SUMMARY OF THE INVENTION

Compounds of the present invention include cell growth inhibitors whichare peptides of Formula I,A-B-D-E-F-(G)_(r)-(K)_(s)-L  (I),and acid salts thereof, wherein A, B, D, E, F, G and K are α-amino acidresidues, and s and r are each, independently, 0 or 1. L is a monovalentradical, such as, for example, an amino group, an N-substituted aminogroup, a β-hydroxylamino group, a hydrazido group, an alkoxy group, athioalkoxy group, an aminoxy group, or an oximato group.

Another aspect of the present invention includes pharmaceuticalcompositions comprising a compound of Formula I and a pharmaceuticallyacceptable carrier.

An additional embodiment of the present invention is a method fortreating cancer in a mammal, such as a human, comprising administeringto the mammal an effective amount of a compound of Formula I in apharmaceutically acceptable composition.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to peptides having antineoplasticactivity. It also includes pharmaceutical compositions comprising thesecompounds and methods for treating cancer in a mammal, including ahuman, by administration of these compositions to the mammal.

Dolastatin 15, a peptide isolated from the sea hare Dolabellaauricularia, is a potent inhibitor of cell growth. This compound,however, is present in trace quantities in the sea hare, and is thusdifficult to isolate. Dolastatin 15 is also expensive to synthesize andsuffers from poor aqueous solubility. As shown herein, however,Dolastatin 15 can serve as a starting point for the development ofcompounds which overcome these disadvantages while retainingantineoplastic activity or exhibiting greater antineoplastic activitythan the natural product. Applicants have discovered that certainstructural modifications of Dolastatin 15 provide compounds with asurprisingly improved therapeutic potential for the treatment ofneoplastic diseases as compared to Dolastatin 10 and Dolastatin 15.Furthermore, the compounds of the present invention can be convenientlysynthesized, as described below in detail.

For the purposes of the present invention, the term “monovalent radical”is intended to mean an electrically neutral molecular fragment capableof forming one covalent bond with a second neutral molecular fragment.Monovalent radicals include the hydrogen atom, alkyl groups, such asmethyl, ethyl and propyl groups, halogen atoms, such as fluorine,chlorine and bromine atoms, aryl groups, such as phenyl and naphthylgroups, and alkoxy groups, such as methoxy and ethoxy groups. Twomonovalent radicals on adjacent sigma-bonded atoms can also togetherform a pi bond between the adjacent atoms. Two monovalent radicals mayalso be linked together, for example, by a polymethylene unit, to form acyclic structure. For example, the unit —N(R)R′, wherein R and R′ areeach a monovalent radical, can, together with the nitrogen atom, form aheterocyclic ring. In addition, two monovalent radicals bonded to thesame atom can together form a divalent radical, such as an oxygen atomor an alkylidene group, for example, a propylidene group.

For the purposes of the present invention, the term “normal alkyl”refers to an unbranched, or straight chain, alkyl group, for example,normal propyl (n-propyl, —CH₂CH₂CH₃).

The compounds of the present invention can be represented by Formula I,A-B-D-E-F-(G)_(r)-(K)_(s)-L  (I),wherein A, B, D, E, F, G, and K are α-amino acid residues; s and r areeach, independently, 0 or 1; and L is a monovalent radical such as anamino group, an N-substituted amino group, a β-hydroxylamino group, ahydrazido group, an alkoxy group, a thioalkoxy group, an aminoxy group,or an oximato group.

The peptides of Formula I are generally composed of L-amino acids butthey can contain one or more D-amino acids. In the following discussion,reference to a particular amino acid includes both enantiomers unless aspecific enantiomer is indicated. The present compounds can also bepresent as salts with physiologically-compatible acids, includinghydrochloric acid, citric acid, tartaric acid, lactic acid, phosphoricacid, methanesulfonic acid, acetic acid, formic acid, maleic acid,fumaric acid, malic acid, succinic acid, malonic acid, sulfuric acid,L-glutamic acid, L-aspartic acid, pyruvic acid, mucic acid, benzoicacid, glucuronic acid, oxalic acid, ascorbic acid and acetylglycine.

The following is a description of the present invention, including adetailed description of individual components and of methods of usingthe claimed compounds.

Compounds of the Present Invention

Identity of A

In one embodiment, A is a proline derivative of Formula II_(a),

where n_(a) is an integer, preferably 0, 1, 2, or 3. R_(a) is amonovalent radical, such as a hydrogen atom or an unsubstituted orfluorine-substituted alkyl group, for example a normal, branched orcyclic C₁-C₃-alkyl group which is, optionally, substituted by from 1 toabout 3 fluorine atoms; suitable examples include methyl, ethyl,isopropyl, 2-fluoroethyl, 2,2,2-trifluoroethyl, 1-methyl-2-fluoroethyl,1-fluoromethyl-2-fluoroethyl or cyclopropyl; methyl, ethyl or isopropylare preferred;

In this embodiment, R¹ _(a) is a monovalent radical, such as a hydrogenatom, an alkyl group, such as a methyl, ethyl or propyl group, or aphenyl group. The phenyl group can be substituted; suitable substituentsinclude one or more halogen atoms, with fluorine, chlorine and bromineatoms preferred, C₁-C₄-alkyl groups, methoxy, ethoxy, trifluoromethyl ornitro groups. R_(a) and R¹ _(a) together can also form a propylenebridge.

R² _(a), R³ _(a), R⁴ _(a) and R⁵ _(a) are each, independently, amonovalent radical, such as a hydrogen atom or an alkyl, preferably,methyl, group.

In another embodiment, A is a substituted glycine derivative of FormulaIII_(a),

where R_(a) has the meaning stated for R_(a) in Formula II_(a) and, R¹_(a) is a monovalent radical, for example, a hydrogen atom or aC₁-C₆-alkyl group, preferably a methyl, ethyl or propyl group.

In this embodiment, R⁶ _(a) is a monovalent radical, such as an alkyl,substituted alkyl, alkenyl, phenyl or substituted phenyl group. Suitableexamples include methoxymethyl, 1-methoxyethyl,1,1-dimethyl-hydroxymethyl, 1-trifluoromethylethyl,1-trifluoromethyl-2,2,2-trifluoroethyl, vinyl, and 1-methylvinyl. Phenylsubstituents can include one or more halogen atoms, preferably fluorine,chlorine or bromine atoms, and alkyl, methoxy, ethoxy, trifluoromethyl,and nitro groups.

When R¹ _(a) is an alkyl group, R⁶ _(a) can also be a C₁-C₆-alkyl,cycloalkyl, unsubstituted benzyl or substituted benzyl group. Suitablebenzyl substituents include one or more halogen atoms, such as fluorine,chlorine or bromine atoms, C₁-C₄-alkyl groups, and methoxy, ethoxy,trifluoromethyl and nitro groups.

R⁷ _(a) is a monovalent radical, preferably a methyl, ethyl or isopropylgroup.

In another embodiment, A is an α-amino acid derivative of FormulaIV_(a),

where m_(a) is an integer, preferably 1 or 2, and R_(a) and R⁷ _(a) havethe meanings stated for these substituents in Formula III_(a).

In another embodiment, A is an α-amino acid derivative of Formula V_(a),

where R_(a) and R⁷ _(a) have the meanings stated for R_(a) and R⁷ _(a)in Formula III_(a).

In a further embodiment, A is a substituted proline derivative ofFormula VI_(a),

where R_(a) and R¹ _(a) have the meanings stated for R_(a) and R¹ _(a)in Formula II_(a), and X_(a) is a monovalent radical, preferably ahydroxyl, alkoxy, for example, methoxy or ethoxy, group or a fluorineatom.

In another embodiment, A is a thiaprolyl derivative of Formula VII_(a),

where R_(a), R¹ _(a), R² _(a), R³ _(a), R⁴ _(a) and R⁵ _(a) have themeanings stated for the respective substituents in Formula II_(a).

In another embodiment, A is a 1,3-dihydroisoindole derivative of FormulaVIII_(a)

where R_(a) has the meaning stated for R_(a) for Formula II_(a).

In another embodiment, A is a 2-azabicyclo[2.2.1]heptane-3-carboxylicacid derivative of Formula IX_(a),

where Z_(a) is a single or double bond and R_(a) has the meaning statedfor Formula II_(a). The 3-carbonyl substituent can have either the exoor endo orientation.

In another embodiment, A is an α-amino acid derivative of Formula X_(a),

where n_(a) has the meaning as stated for n_(a) for Formula II_(a), andR⁷ _(a) and R_(a) have the meanings as stated for R⁷ _(a) and R_(a) forFormula III_(a).Identity of B

B is a valyl, isoleucyl, allo-isoleucyl, norvalyl, 2-tert-butylglycyl or2-ethylglycyl residue. B can also be an α-amino acid residue of FormulaII_(b),

in which R¹ _(b) and R² _(b) are each a monovalent radical. R¹ _(b) is,preferably, a hydrogen atom and R² _(b) is, for example, an alkyl,alkoxyalkyl or alkenyl group. In preferred embodiments, R² _(b) is acyclopropyl group, a normal or branched butyl, preferablytertiary-butyl, group, a methoxymethyl group, a 1-methoxyethyl group ora 1-methylvinyl group. Additionally, R¹ _(b) and R² _(b) together can bean isopropylidene group.Identity of D

D is an N-alkylvalyl, N-alkyl-2-ethylglycyl, N-alkyl-2-tert-butylglycyl,N-alkyl-norleucyl, N-alkyl-isoleucyl, N-alkyl-allo-isoleucyl orN-alkyl-norvalyl residue, where the N-alkyl group is preferably a methylgroup or an ethyl group.

In another embodiment, D is an α-amino acid residue of Formula II_(d),

where R_(d) has the meaning stated for R_(a) in Formula III_(a), R¹ _(d)is a monovalent radical, preferably a hydrogen atom, and R² _(d) is amonovalent radical, for example, an alkyl, alkoxyalkyl or alkenyl group.In preferred embodiments, R² _(d) is a cyclopropyl group, a normal orbranched butyl, preferably tertiary-butyl, group, a methoxymethyl group,a 1-methoxyethyl group or a 1-methylvinyl group. such as a cyclopropylgroup, a methoxymethyl group, a 1-methoxyethyl group or a 1-methylvinylgroup. Additionally, R¹ _(d) and R² _(d) together can form anisopropylidene group.

Alternatively, D can be a proline derivative of Formula III_(d),

where n_(d) is an integer, for example, 1 or 2, and R³ _(d) has themeaning stated for R¹ _(a) in Formula III_(a). X_(d) is a monovalentradical, preferably a hydrogen atom, and, in the case where n_(d) equals1, can also be a hydroxy or alkoxy, for example, methoxy or ethoxy,group or a fluorine atom.Identity of E

E is a prolyl, thiazolidinyl-4-carbonyl, homoprolyl or hydroxyprolylresidue, or a cyclic α-amino carboxylic acid residue of Formula II_(e),

where n_(e) is an integer, preferably 0, 1 or 2. R¹ _(e) has the meaningstated for R¹ _(a) in Formula III_(a). R² _(e) and R³ _(e) are each amonovalent radical, and can be, independently, a hydrogen atom or analkyl, preferably methyl, group. R⁴ _(e) is a monovalent radical,preferably a hydrogen atom, a hydroxy, alkoxy, for example, methoxy orethoxy, group or a fluorine atom. R⁵ _(e) is a monovalent radical,preferably a hydrogen atom or a fluorine atom. In the case where n_(e)is 1, R³ _(e) and R⁴ _(e) can together form a double bond, or R⁴ _(e)and R⁵ _(e) can together be a double-bonded oxygen radical. In the casewhere n_(e) has the value 1 or 2, R¹ _(e) and R² _(e) can together forma double bond.

In another embodiment, E is a 2- or 3-amino-cyclopentanecarboxylic acidresidue of Formula III_(e),

where R_(e) is an alkyl group, such as methyl or ethyl, and R¹ _(e) hasthe meaning stated for R¹ _(a) in Formula III_(a).Identity of F

F is a prolyl, thiazolidinyl-4-carbonyl, homoprolyl or hydroxyprolylresidue. F can also be a cyclic α-amino acid residue of Formula II_(f),

where n_(f) is an integer, preferably 0, 1 or 2. R¹ _(f) has the meaningstated for R¹ _(a) in Formula III_(a). R² _(f) and R³ _(f) are each amonovalent radical, and can be, independently, a hydrogen atom or analkyl, preferably methyl, group. R⁴ _(f) is a monovalent radical,preferably a hydrogen atom, a hydroxy, alkoxy, for example, methoxy orethoxy, group or a fluorine atom. R⁵ _(f) is a monovalent radical,preferably a hydrogen atom or a fluorine atom. In the case where n_(f)has the value 1, R³ _(f) and R⁴ _(f) together can form a double bond orR⁴ _(f) and R⁵ _(f) can together be a double-bonded oxygen radical. Inthe case where n_(f) has the value 1 or 2, R¹ _(f) and R² _(f) cantogether form a double bond.

In another embodiment, F is a 2- or 3-amino-cyclopentanecarboxylic acidresidue of Formula III_(f)

where R_(f) is a monovalent radical, such as a methyl or ethyl group,and R¹ _(f) has the meaning stated for R¹ _(a) in Formula III_(a).

In another embodiment, F is an N-alkylglycyl or N-alkylalanyl residue,and the alkyl group is, preferably, a methyl group or an ethyl group.

Identity of G

G is an α-amino acid residue of Formula II_(g),

wherein R¹ _(g) is a hydrogen atom, or an alkyl group, for example,methyl, ethyl or n-propyl. R² _(g) can be, for example, a hydrogen atom,or an alkyl, arylalkyl, heteroarylalkyl or aryl group. Preferably, R²_(g) is an ethyl, isopropyl, tert-butyl, isobutyl, 2-methylpropyl,cyclohexylmethyl, benzyl, thiazolyl-2-methyl, pyridyl-2-methyl, n-butyl,2,2-dimethylpropyl, naphthylmethyl, or n-propyl group, or a substitutedor unsubstituted phenyl group. Suitable phenyl substituents include oneor more halogen, preferably fluorine, chlorine or bromine, atoms,C₁-C₄-alkyl groups, methoxy, ethoxy, nitro or trifluoromethyl groups ora dioxomethylene group. Alternately, R¹ _(g) and R² _(g) can, togetherwith the α-carbon atom, form a cyclopentane or cyclohexane ring or abenzo-fused cyclopentane ring, such as, for example, the indanyl group.Identity of K

K is an α-amino acid residue of Formula II_(k),

wherein R¹ _(k) has the identity stated for R¹ _(g) in Formula II_(g),and R² _(k) has the identity stated for R² _(g) in Formula II_(g).Identity of L

In one embodiment, L is an amino or substituted amino group of FormulaII_(l),

where R¹ _(l) is a monovalent radical, such as a hydrogen atom, a normalor branched, saturated or unsaturated C₁-C₁₈-alkoxy group, a substitutedor unsubstituted aryloxy group, a substituted or unsubstitutedaryl-C₁-C₆-alkoxy group, or a substituted or unsubstitutedaryloxy-C₁-C₆-alkoxy or heteroaryl-C₁-C₆-alkoxy group. The aryl group ispreferably a phenyl or naphthyl group. The heteroaryl group is a 5- or6-membered, preferably nitrogen-, oxygen- or sulfur-containing, ringsystem, such as, for example, a heteroaryl group derived from imidazole,isoxazole, isothiazole, thiazole, oxazole, pyrazole, thiophene, furan,pyrrole, 1,2,4- or 1,2,3-triazole, pyrazine, indole, benzofuran,benzothiophene, indole, isoindole, indazole, quinoline, pyridazine,pyrimidine, benzimidazole, benzopyran, benzothiazole, oxadiazole,thiadiazole or pyridine. Suitable aryl substituents include one or morehalogen, preferably fluorine, bromine or chlorine, atoms, C₁-C₄-alkylgroups, methoxy, ethoxy or trifluoromethyl groups, a dioxymethylenegroup or nitro groups.

R² _(l) is a monovalent radical, such as a hydrogen atom, a normal orbranched, saturated or unsaturated C₁-C₁₈-alkyl group, aC₃-C₁₀-cycloalkyl group, a substituted or unsubstituted aryl group, or asubstituted or unsubstituted heteroaryl group. The aryl group ispreferably a phenyl or naphthyl group. The heteroaryl group is a 5- or6-membered, preferably nitrogen-, oxygen- or sulfur-containing, ringsystem, such as, for example, a heteroaryl group derived from imidazole,isoxazole, isothiazole, thiazole, oxazole, pyrazole, thiophene, furan,pyrrole, 1,2,4- or 1,2,3-triazole, pyrazine, indole, benzofuran,benzothiophene, indole, isoindole, indazole, quinoline, pyridazine,pyrimidine, benzimidazole, benzopyran, benzothiazole, oxadiazole,thiadiazole or pyridine. Suitable aryl substituents include one or morehalogen, preferably fluorine, bromine or chlorine, atoms, C₁-C₄-alkylgroups, methoxy, ethoxy or trifluoromethyl groups, a dioxymethylenegroup or nitro groups.

R² _(l) can, alternately, be of Formula II_(r),

where a_(l) is an integer, such as 0, 1, 2, 3, 4 or 5. R³ _(l) is amonovalent radical, preferably a lower alkyl group, such as a methyl,ethyl, propyl or isopropyl group. R⁴ _(l) is a monovalent radical, whichcan be a saturated or partially unsaturated carbocyclic systemcomprising from about 3 to about 10 carbon atoms, a substituted orunsubstituted aryl or heteroaryl group, with aryl and heteroaryl andpreferred substituents having the meaning stated for R² _(l) , inFormula II_(l).

R² _(l) can also be a substituent of Formula III_(r),—(CH₂)₂—W_(l)—R⁵ _(l)  (III_(r)),wherein W_(l) is an oxygen or sulfur atom or an N—R⁶ _(l) group. R⁵ _(l)is a monovalent radical, such as a hydrogen atom, a C₁-C₄-alkyl orC₃-C₇-cycloalkyl group or a substituted or unsubstituted aryl orarylmethyl group, with aryl and its preferred substituents having themeaning stated for R² _(l) from Formula II_(l). R⁶ _(l) is a monovalentradical, preferably a hydrogen atom, a C₁-C₄-alkyl group or aC₃-C₇-cycloalkyl group, a C₁-C₁₈-alkanoyl group, a benzoyl group or asubstituted or unsubstituted aryl or arylmethyl group, with aryl and itspreferred substituents having the meaning stated for R² _(l) in FormulaII_(l).

R² _(l) can, alternately, be a substituent of Formula IV_(r),—(CH₂)_(b) _(l) -Z_(l)  (IV_(r)),where b_(l) is an integer, preferably 2, 3 or 4. Z_(l) can be amonovalent radical such as a formyl, aminocarbonyl or hydrazinocarbonylgroup, or a cyclic or acyclic acetal or thioacetal group.

R² _(l) can also be a substituent of Formula V_(r),

in which b_(l) has the above-mentioned meaning. R⁷ _(l) can be amonovalent radical, such as a polyglycol group of the formula—O—(CH₂—CH₂—O)_(d) _(l) —CH₃, where d_(l) is an integer, preferably inthe range from about 2 to about 4 or from about 40 to about 90.

R² _(l) can further be a carbohydrate of Formula VI_(r),

where R⁸ _(l) is a monovalent radical, such as a hydrogen atom, aC₁-C₄-alkanoyl or alkyl group, a benzoyl group or a benzyl group.

L can also be a β-hydroxylamino group of Formula III_(l),

where R⁹ _(l) is a monovalent radical such as a hydrogen atom, aC₁-C₆-alkyl group or a substituted or unsubstituted aryl group, witharyl and its preferred substituents having the meaning stated for R²_(l). R¹⁰ _(l) is a monovalent radical, preferably a hydrogen atom,alkyl, for example, methyl, or a phenyl group.

When r and/or s is 1, L can also be an amino group of Formula IV_(l),

where R² _(l) and R⁴ _(l) are each a monovalent radical. R² _(l) and R⁴_(l) can also be linked by a carbon-carbon bond.

Another subclass of compounds of this invention includes peptides ofFormula I wherein L is a hydrazido group of Formula V_(l),

and R¹¹ _(l) is a monovalent radical, preferably a hydrogen atom. R¹²_(l) can be a monovalent radical such as a hydrogen atom, a normal orbranched C₁-C₈-alkyl group, a C₃-C₈-cycloalkyl group, aC₃-C₈-cycloalkyl-C₁-C₄-alkyl group or a substituted or unsubstitutedaryl, heteroaryl, aryl-C₁-C₄-alkyl or heteroaryl-C₁-C₄-alkyl group,where aryl, heteroaryl and their preferred substituents can be selectedfrom among the options listed for R² _(l).

When r and/or s is 1, R¹¹ _(l) can also be selected from among theoptions listed above for R¹² _(l), and the two radicals together canadditionally form a propylene or butylene bridge.

Another subclass of compounds of this invention includes peptides ofFormula I wherein L is a monovalent radical of the formula —O—R¹³ _(l)or the formula —S—R¹³ _(l), where R¹³ _(l) is a monovalent radical, suchas a C₃-C₁₀-cycloalkyl group, a normal or branched C₂-C₁₆-alkenylmethylgroup or a C₁-C₁₆-alkyl group which can be substituted by from 1 toabout 5 halogen, preferably fluorine, atoms.

R¹³ _(l) can also be the radical —(CH₂)_(e)—R¹⁴ _(l), where e is aninteger, preferably 1, 2 or 3. R¹⁴ _(l) is a monovalent radical,preferably a saturated or partially unsaturated C₃-C₁₀-carbocycle.

R¹³ _(l) can further be the monvalent radical—[CH₂—CH═C(CH₃)—CH₂]_(f)—H, where f is an integer, preferably 1, 2, 3 or4.

R¹³ _(l) can also be the radical —[CH₂—CH₂O]_(g)—CH₃, where g is aninteger, preferably in the range from 1 to about 5.

R¹³ _(l) can also be the radical —(CH₂)_(h)-aryl or—(CH₂)_(h)-heteroaryl, where aryl and heteroaryl can also be substitutedand, along with their preferred substituents, can be selected from thegroup listed for R² _(l). h is an integer, preferably 0, 1, 2 or 3.

R¹³ _(l) can further be the radical —(CH₂)_(b)—W_(l)—R⁵ _(l). b, W_(l)and R⁵ _(l) can each be selected from among the options described forFormula IV_(l).

Another subclass of compounds of this invention includes peptides ofFormula in which L is an aminoxy group of the formula —O—N(R¹⁵ _(l))(R¹⁶_(l)), where R¹⁵ _(l) and R¹⁶ _(l) are each a monovalent radical, whichcan independently be a hydrogen atom, a normal or branched C₁-C₈-alkylgroup, which can be substituted by halogen, preferably fluorine, atoms,a C₃-C₈-cycloalkyl group, a C₃-C₈-cycloalkyl-C₁-C₄-alkyl group, asubstituted or unsubstituted aryl or heteroaryl group or a substitutedor unsubstituted aryl-C₁-C₄-alkyl group. Aryl and heteroaryl groups andthe preferred substituents thereof can be selected from the optionslisted for R² _(l). R¹⁶ _(l) can be selected from among the optionslisted for R¹⁵ _(l). Additionally, R¹⁵ _(l) and R¹⁶ _(l) can togetherform a 5-, 6- or 7-membered heterocycle. The compounds of the presentinvention further comprise the salts of the compounds described abovewith physiologically tolerated acids.

Another subclass of compounds of this invention includes peptides ofFormula I wherein L is an oximato group of the formula —O—N═C(R¹⁵_(l))(R¹⁶ _(l)), R¹⁵ _(l) and R¹⁶ _(l) can be selected from among theoptions listed above and, additionally, can together form a cyclicsystem comprising, preferably, from about 3 to about 7 ring atoms. Thiscyclic system can additionally be fused to one or more aromatic rings.Particularly preferred cyclic systems are shown below.

In one embodiment, the invention provides compounds of Formula I whereinA is an amino acid derivative selected from among N-alkyl-D-prolyl,N-alkyl-L-prolyl, N-alkyl-D-piperidine-2-carbonyl,N-alkyl-L-piperidine-2-carbonyl, N,N-dialkyl-D-2-ethyl-2-phenylglycyland N,N-dialkyl-L-2-ethyl-2-phenylglycyl, wherein alkyl is methyl, ethylor isopropyl; and B is a valyl, isoleucyl or 2-t-butyl-L-glycyl residue.

Preferred compounds of the invention include compounds of Formula Iwherein r and s are each 0. A is an amino acid derivative selected fromamong D-N-methyl-piperidine-2-carbonyl,L-N-methyl-piperidine-2-carbonyl, N,N-dimethylamino-iso-butyryl,N-methyl-L-prolyl, N-methyl-L-thiazolidine-4-carbonyl,N,N-dimethyl-glycyl, L-prolyl, L-piperidine-2-carbonyl,N-propyl-D-piperidine-2-carbonyl, D-piperidine-2-carbonyl,N-ethyl-D-piperidine-2-carbonyl,N-methyl-[2,2,5,5-tetramethyl]-L-thiazolidine-2-carbonyl,N-isopropyl-D-piperidine-2-carbonyl, N,N-dimethyl-2-cyclopropylglycyl,N,N-dimethyl-L-2-ethyl-2-phenylglycyl,N,N-dimethyl-D-2-ethyl-2-phenylglycyl, D-prolyl, N-methyl-D-prolyl,N,N-dimethyl-2-(2-fluorophenyl)glycyl,1-aza-[3,3,0]bicyclooctyl-5-carbonyl,N,N-dimethyl-2-[4-fluoro]phenyl-glycyl,N-methyl-[2,2,5,5-tetramethyl]-thiazolidine-2-carbonyl,2-(R,S)-ethyl-2-phenylglycyl, D,L-1-aminoindane-1-carbonyl,N,N-dimethyl-2-(R,S)-methyl-2-phenylglycyl, 2-[N,N-dimethylamino]indane-2-carbonyl,5-[N,N-dimethylamino]-5,6,7,8-tetrahydronaphthalene-5-carbonyl,N-isopropyl-2-(R,S)-ethyl-2-phenylglycyl,1-[N,N-dimethylamino]indane-2-carbonyl,N,N-dimethyl-2-propyl-2-phenylglycyl,N,N-dimethyl-2-[4-methoxy]phenyl-glycyl, N-methyl-3-hydroxy-D,L-valyl,N,N-dimethyl-D,L-2-isopropyl-2-phenylglycyl,N-methylpiperidine-2-carbonyl, N-methyl-L-prolyl,N-methyl-1,2,3,4-tetrahydroisoquinoline-1-carbonyl,N-methylazetidine-2-carbonyl, N-isopropylazetidine-2-carbonyl,N,N-dimethyl-[O-methyl]seryl, N,N-dimethyl-[O-methyl]threonyl,N-methyl-1,2,3,4-tetrahydroisoquinoline-3-carbonyl,1-[N,N-dimethylamino]cyclohexyl-1-carbonyl,1-[N,N-dimethylamino]cyclopentyl-1-carbonyl and1,2,3,4-tetrahydroisoquinoline-3-carbonyl. B is valyl, isoleucyl or2-tert-butylglycyl. D is N-methylvalyl, N-methyl-2-t-butylglycyl orN-methylisoleucyl. E and F are each, independently, prolyl, thiaprolyl,homoprolyl, hydroxyprolyl, 3,4-didehydroprolyl, 4-fluoroprolyl, and3-methylprolyl. L is an alkoxy group or an amino group of the formula R¹_(l)—N—R² _(l), wherein R¹ _(l) and R² _(l) are independently selectedfrom the group consisting of hydrogen, alkoxy, hydroxy, alkyl andalkylaryl.

In a particularly preferred subset of the compounds of the invention, rand s are each 0. A is an amino acid derivative selected from amongD-N-methyl-piperidine-2-carbonyl, N-ethyl-D-piperidine-2-carbonyl,N-isopropyl-D-piperidine-2-carbonyl, N,N-dimethyl-2-cyclopropyl-glycyl,N-methyl-D-prolyl, 1-aza-[3,3,0]bicyclooctyl-5-carbonyl,N-methyl-[2,2,5,5-tetramethyl]-thiazolidine-2-carbonyl,2-(R,S)-ethyl-2-phenylglycyl, D,L-1-aminoindane-1-carbonyl,N,N-dimethyl-2-(R,S)-methyl-2-phenylglycyl,5-[N,N-dimethylamino]-5,6,7,8-tetrahydro-naphthalene-5-carbonyl,1-[N,N-dimethylamino]indane-2-carbonyl,N,N-dimethyl-2-propyl-2-phenylglycyl,N,N-dimethyl-L-2-ethyl-2-phenylglycyl,N,N-dimethyl-D-2-ethyl-2-phenylglycyl, N-methyl-3-hydroxy-D,L-valyl,N,N-dimethyl-D,L-2-isopropyl-2-phenylglycyl,N-methyl-piperidine-2-carbonyl, N-methyl-D,L-prolyl,N-methyl-1,2,3,4-tetrahydroisoquinoline-1-carbonyl,N-methylazetidine-2-carbonyl, N-isopropylazetidine-2-carbonyl,N,N-dimethyl-[O-methyl]seryl, 1-[N,N-dimethylamino]cyclohexyl-1-carbonyland 1-[N,N-dimethylamino]cyclopentyl-1-carbonyl. B is valyl; D isN-methylvalyl; and E and F are each prolyl. L is a C₁-C₆-alkoxy group oran amino group of the formula R¹ _(l)—N—R² _(l), wherein R¹ _(l) and R²_(l) are each independently selected from the group consisting ofhydrogen, C₁-C₆-alkoxy, hydroxy, normal, cyclic or branchedC₁-C₁₂-alkyl, and phenylalkyl.

Synthetic Methods

The compounds of the present invention can be prepared by known methodsof peptide synthesis. Thus, the peptides can be assembled sequentiallyfrom individual amino acids or by linking suitable small peptidefragments. In sequential assembly, the peptide chain is extendedstepwise, starting at the C-terminus, by one amino acid per step. Infragment coupling, fragments of different lengths can be linkedtogether, and the fragments in turn can be obtained by sequentialassembly from amino acids or by fragment coupling of still shorterpeptides.

In both sequential assembly and fragment coupling it is necessary tolink the units by forming an amide linkage, which can be accomplishedvia a variety of enzymatic and chemical methods. Chemical methods forforming the amide linkage are described in detail in standard referenceson peptide chemistry, including Müller, Methoden der organischen ChemieVol. XV/2, 1-364, Thieme Verlag, Stuttgart, (1974); Stewart and Young,Solid Phase Peptide Synthesis, 31-34 and 71-82, Pierce Chemical Company,Rockford, Ill. (1984); Bodanszky et al., Peptide Synthesis, 85-128, JohnWiley & Sons, New York, (1976). Preferred methods include the azidemethod, the symmetric and mixed anhydride method, the use of in situgenerated or preformed active esters, the use of urethane protectedN-carboxy anhydrides of amino acids and the formation of the amidelinkage using coupling reagents, such as carboxylic acid activators,especially dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide(DIC), 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), pivaloylchloride, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride(EDCI), n-propanephosphonic anhydride (PPA),N,N-bis(2-oxo-oxazolidinyl)amidophosphoryl chloride (BOP-Cl),bromo-tris(pyrrolidino)phosphonium hexafluorophosphate (PyBrop),diphenylphosphoryl azide (DPPA), Castro's reagent (BOP, PyBop),O-benzotriazolyl-N,N,N′,N′-tetramethyluronium salts (HBTU),O-azabenzotriazolyl-N,N,N′,N′-tetramethyluronium salts (HATU),diethylphosphoryl cyanide (DEPCN),2,5-diphenyl-2,3-dihydro-3-oxo-4-hydroxythiophene dioxide (Steglich'sreagent; HOTDO), and 1,1′-carbonyldiimidazole (CDI). The couplingreagents can be employed alone or in combination with additives such asN,N-dimethyl-4-aminopyridine (DMAP), N-hydroxy-benzotriazole (HOBt),N-hydroxyazabenzotriazole (HOAt), N-hydroxybenzotriazine (HOOBt),N-hydroxysuccinimide (HOSu) or 2-hydroxypyridine.

Although the use of protecting groups is generally not necessary inenzymatic peptide synthesis, reversible protection of reactive groupsnot involved in formation of the amide linkage is necessary for bothreactants in chemical synthesis. Three conventional protective grouptechniques are preferred for chemical peptide synthesis: thebenzyloxycarbonyl (Z), the t-butoxycarbonyl (Boc) and the9-fluorenylmethoxycarbonyl (Fmoc) techniques. Identified in each case isthe protective group on the α-amino group of the chain-extending unit. Adetailed review of amino-acid protective groups is given by Müller,Methoden der organischen Chemie Vol. XV/1, pp 20-906, Thieme Verlag,Stuttgart (1974). The units employed for assembling the peptide chaincan be reacted in solution, in suspension or by a method similar to thatdescribed by Merrifield, J. Am. Chem. Soc. 85: (1963) 2149.

Solvents suitable for peptide synthesis include any solvent which isinert under the reaction conditions, especially water,N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile,dichloromethane (DCM), 1,4-dioxane, tetrahydrofuran (THF),N-methyl-2-pyrrolidone (NMP) and mixtures of these solvents.

Peptide synthesis on the polymeric support can be carried out in asuitable inert organic solvent in which the amino acid derivativesstarting materials are soluble. However, preferred solvents additionallyhave resin-swelling properties, such as DMF, DCM, NMP, acetonitrile andDMSO, and mixtures of these solvents. Following synthesis, the peptideis removed from the polymeric support. The conditions under which thiscleavage is accomplished for various resin types are disclosed in theliterature. The cleavage reactions most commonly used are acid- orpalladium-catalyzed, the former being conducted in, for example, liquidanhydrous hydrogen fluoride, anhydrous trifluoromethanesulfonic acid,dilute or concentrated trifluoroacetic acid, and aceticacid/dichloromethane/trifluoroethanol mixtures. The latter can becarried out in THF or THF-DCM-mixtures in the presence of a weak base,such as morpholine. Certain protecting groups are also cleaved off underthese conditions.

Partial deprotection of the peptide may also be necessary prior tocertain derivatization reactions. For example, peptides dialkylated atthe N-terminus can be prepared by coupling the appropriateN,N-di-alkylamino acid to the peptide in solution or on the polymericsupport, by reductive alkylation of the resin-bound peptide in DMF/1%acetic acid with NaCNBH₃ and the appropriate aldehyde or byhydrogenation of the peptide in solution in the presence of theappropriate aldehyde or ketone and Pd/carbon.

The various non-naturally occurring amino acids as well as the variousnon-amino acid moieties disclosed herein can be obtained from commercialsources or synthesized from commercially available staring materialsusing methods known in the art. For example, amino acid building blockswith R¹ and R² groups can be prepared according to the method describedby Wuensch and Weyl, Methoden der Organische Chemie, vol. XV, SpringerVerlag: Stuttgart, p. 306 (1974) and references cited therein.

Methods of Use of the Claimed Compounds

In another embodiment, the present invention comprises a method forpartially or totally inhibiting formation of, or otherwise treating(e.g., reversing or inhibiting the further development of) solid tumors(e.g., tumors of the lung, breast, colon, prostate, bladder, rectum, orendometrial tumors) or hematological malignancies (e.g., leukemias,lymphomas) in a mammal, for example, a human, by administering to themammal a therapeutically effective amount of a compound or a combinationof compounds of Formula I. The compound(s) may be administered alone orin a pharmaceutical composition comprising the compound(s) and anacceptable carrier or diluent. Administration can be by any of the meanswhich are conventional for pharmaceutical, preferably oncological,agents, including oral and parenteral means, such as subcutaneously,intravenously, intramuscularly and intraperitoneally, nasally orrectally. The compounds may be administered alone or in the form ofpharmaceutical compositions containing a compound or compounds ofFormula I together with a pharmaceutically accepted carrier appropriatefor the desired route of administration. Such pharmaceuticalcompositions may be combination products, i.e., they may also containother therapeutically active ingredients.

The dosage to be administered to the mammal, such as a human, willcontain a therapeutically effective amount of a compound describedherein. As used herein, “therapeutically effective amount” is an amountsufficient to inhibit (partially or totally) formation of a tumor or ahematological malignancy or to reverse development of a solid tumor orother malignancy or prevent or reduce its further progression. For aparticular condition or method of treatment, the dosage is determinedempirically, using known methods, and will depend upon factors such asthe biological activity of the particular compound employed; the meansof administration; the age, health and body weight of the recipient; thenature and extent of the symptoms; the frequency of treatment; theadministration of other therapies; and the effect desired. A typicaldaily dose will be from about 0.05 to about 50 milligrams per kilogramof body weight by oral administration and from about 0.01 to about 20milligrams per kilogram of body weight by parenteral administration.

The compounds of the present invention can be administered inconventional solid or liquid pharmaceutical administration forms, forexample, uncoated or (film-)coated tablets, capsules, powders, granules,suppositories or solutions. These are produced in a conventional manner.The active substances can for this purpose be processed withconventional pharmaceutical aids such as tablet binders, fillers,preservatives, tablet disintegrants, flow regulators, plasticizers,wetting agents, dispersants, emulsifiers, solvents, sustained releasecompositions, antioxidants and/or propellant gases (cf. H. Sücker etal.: Pharmazeutische Technologic, Thieme-Verlag, Stuttgart, 1978). Theadministration forms obtained in this way typically contain from about 1to about 90% by weight of the active substance.

The present invention will now be illustrated by the following examples,which are not limiting.

EXAMPLES

The proteinogenous amino acids are abbreviated in the examples using theknown three-letter code. Other abbreviations employed are:TFA=trifluoroacetic acid, Ac=acetic acid, DCM=dichloromethane,DMSO=dimethylsulfoxide, Bu=butyl, Et=ethyl, Me=methyl, Bzl=benzyl. Inthe compounds listed, all proteinogenous amino acids are L-amino acidsunless otherwise noted. Other abbreviations used:Me₂Val=N,N-dimethylvaline, MeVal=N-methylvaline, Bn=benzyl,Me₂Aib=[2-N,N-dimethylamino]-isobutyric acid.

General Procedures

The peptides of the invention are synthesized either by classicalsolution synthesis using standard Z- and Boc-methodology as describedabove or by standard methods of solid-phase synthesis using Boc and Fmocprotective group techniques.

In the case of solid phase synthesis, the N,N-dialkyl-penta- orhexapeptide acids are liberated from the solid support and furthercoupled with the corresponding C-terminal amines in solution. BOP-Cl andPyBrop were used as reagents for coupling of the amino acid followingthe N-methylamino acids. The reaction times were correspondinglyincreased. For reductive alkylation of the N-terminus, the peptide-resinwas deprotected at the N terminus and then reacted with a 3-fold molarexcess of aldehyde or ketone in DMF/1% acetic acid with addition of 3equivalents of NaCNBH₃. After the reaction was complete (negative Kaisertest) the resin was washed several times with water, isopropanol, DMFand dichloromethane.

In solution synthesis, the use of either Boc-protected amino acid NCAs(N-tert.-butyloxycarbonyl-amino acid-N-carboxy-anhydrides), Z-protectedamino acid NCAs (N-benzyloxycarbonyl-amino acid-N-carboxy-anhydrides),or the use of pivaloyl chloride as condensing agent respectively is mostadvantageous for coupling of the amino acid following the N-methylaminoacids. Reductive alkylation of the N terminus can e.g. be achieved byreaction of the N-terminally deprotected peptides or amino acids withthe corresponding aldehydes or ketones using NaCNBH₃ or hydrogen-Pd/C.

Valyl-N-methylvalyl-prolyl-prolylbenzylamide hydrochloride for examplewas prepared according to methods disclosed in German Patent ApplicationNo. DE 19527575 A1.

Purification and Characterization of the Peptides

Peptide purification was carried out by get chromatography (SEPHADEXG-10, G-15/10% HOAc, SEPHADEX LH₂0/MeOH), medium pressure chromatography(stationary phase: HD-SIL C-18, 20-45 micron, 100 Angstrom; mobilephase: gradient with A=0.1% TFA/MeOH, B=0.1% TFA/water), preparativeHPLC (stationary phase: Waters Delta-Pak C-18, 15 micron, 100 Angstrom;mobile phase: gradient with A=0.1% TFA/MeOH, B=0.1% TFA/water), or bycrystallization.

The purity of the resulting products was determined by analytical HPLC(stationary phase: 100 2.1 mm VYDAC C-18, 5 micron, 300 A; mobile phase:acetonitrile-water gradient, buffered with 0.1% TFA, 40° C.; or 3.9 mmVYDAC C-18, 30° C.). Characterization was by fast atom bombardment massspectroscopy and NMR-spectroscopy.

Example 1 Synthesis of[N-Methyl-L-piperidine-2-carbonyl]-Val-MeVal-Pro-Pro-NHBn (Compound 1)and [N-Methyl-D-piperidine-2-carbonyl]-Val-MeVal-Pro-Pro-NHBn (Compound2)

Preparation of N-methyl-piperidine-2-carboxylic acid

N-Methyl-piperidine-2-carboxylic acid ethyl ester (5.1 g) was dissolvedin a mixture of 100 ml methanol and 10 ml water. NaOH (8 g) was addedand the reaction mixture was stirred at room temperature overnight. Thesolution was then neutralized with hydrochloric acid, evaporated todryness, and evaporated four times with toluene. The resulting powderyresidue was used directly in the next step.

Preparation of [N-Methyl-piperidine-2-carbonyl]-Val-MeVal-Pro-Pro-NHBn

The residue prepared as described above (5.05 g) andH-Val-MeVal-Pro-Pro-NHBn×HCl (4.88 g) were dissolved in 50 ml dry DMF.After cooling the solution in an ice bath, 1.52 g DEPCN and 2.66 mltriethylamine were added. The reaction mixture was stirred at 0° C. for2 h and then at room temperature overnight. The DMF was removed byevaporation under reduced pressure. The residue was diluted withdichloromethane and the organic phase was washed with aqueoushydrochloric acid (pH 2) and water, dried over sodium sulfate andevaporated to dryness. The diastereomeric mixture was then separated byflash chromatography with a gradient using heptane/ethyl acetate anddichloromethane/methanol. Under the HPLC conditions described in theprevious section (C-18 reverse phase) isomer 1 has a retention time of14.9 minutes, and isomer 2 has a retention time of 15.8 minutes. Bothisomers were characterized by fast atom bombardment mass spectrometry([M+H]+=639).

Example 2 Preparation of Me₂Aib-Val-MeVal-Pro-Pro-NHBn (Compound 3)

Preparation of 2-[N,N-dimethylamino]-isobutyric acid

2-Amino-isobutyric acid (10.3 g) was dissolved in 200 ml methanol. Afteraddition of 25 ml aqueous formaldehyde and 1 g 10% Pd/C, the reactionmixture was hydrogenated overnight at room temperature. The catalyst wasfiltered, and the filtrate was evaporated to dryness. The residue wascrystallized from isopropanol to give 4.8 g of the desired product.

Preparation of Me₂Aib-Val-MeVal-Pro-Pro-NHBn×HCl

2-[N,N-Dimethylamino]-isobutyric acid (1.3 g, 10 mmol) and 5.5 g (10mmol) H-Val-MeVal-Pro-Pro-NHBn×HCl were dissolved in 50 ml dry DMF.After cooling to 0° C., 1.6 g DEPCN (10 mmol) and 2.9 ml triethylaminewere added to the reaction mixture. The resulting mixture was stirred at0° C. for 2 h and at room temperature overnight. Ice water (50 mL) wasthen added, and the resulting mixture was extracted twice with diethylether. The ether extracts were washed with 1 N NaOH (1×) and aqueousNaCl (3×), then dried over sodium sulfate and evaporated to drynessunder reduced pressure. The product was crystallized from 100 ml diethylether with HCl/ether, and recrystallized from acetone to give 1.2 g ofthe desired product, which was characterized by fast atom bombardmentmass spectrometry ([M+H]+=627).

Example 3 Preparation of[N,N-dimethyl-2-ethyl-2-phenylglycyl]-Val-MeVal-Pro-Pro-NHBn×HCl(Compound 4)

Preparation of[N,N-dimethyl-2-ethyl-2-phenylglycyl]-Val-MeVal-Pro-Pro-NHBn×HCl

2.07 g (10 mmol) N,N-Dimethyl-2-ethyl-2-phenylglycine and 5.5 g (10mmol) H-Val-MeVal-Pro-Pro-NHBn×HCl were dissolved in 100 ml dry DMF.After cooling to 0° C., 1.6 g DEPCN (10 mmol) and 2.9 ml triethylaminewere added. The reaction mixture was stirred at 0° C. for 2 h and atroom temperature overnight, then worked up as described above. The crudeproduct was crystallized from diethyl ether with HCl/ether to give 4 gof the desired product, which was characterized by fast atom bombardmentmass spectrometry ([M+H]+=703).

Example 4 Preparation of [N-Methyl-D-Pro]-Val-MeVal-Pro-Pro-NHBn(Compound 5)

Preparation of Z-D-Pro-Val-MeVal-Pro-Pro-NHBn

3.74 g Z-D-Pro-OH (15 mmol, BACHEM) and 8.25 gH-Val-MeVal-Pro-Pro-NHBn×HCl (15 mmol) were dissolved in 80 ml dry DMF.After cooling to 0° C., 2.4 g DEPCN (2.25 ml, 15 mmol) and 4.2 mltriethylamine (30 mmol) were added. The reaction mixture was stirred at0° C. for several hours and room temperature overnight, then the DMF wasevaporated under reduced pressure. The residue was diluted with ethylacetate and thoroughly washed with dilute aqueous HCl (pH 2), water,dilute aqueous NaOH (pH 9-10), and water. The organic phase was driedover sodium sulfate and evaporated to dryness to yield 9.2 g of thedesired protected pentapeptide.

Preparation of D-Pro-Val-MeVal-Pro-Pro-NHBn×HCl

8.2 g (11 mmol) Z-D-Pro-Val-MeVal-Pro-Pro-NHBn was dissolved in 70 mlmethanol. After addition of 0.7 ml concentrated hydrochloric acid and0.3 g 10% Palladium/charcoal to the solution, the resulting mixture washydrogenated. Filtration and evaporation of the solvent gave a residuewhich was dissolved in water, adjusted to pH 2 and extracted twice withethyl acetate. The aqueous phase was adjusted to pH 9-10 and extractedtwice with dichloromethane. The organic extracts were evaporated and theresidue was redissolved in diethylether and crystallized by addition ofHCl/ether as the hydrochloride salt to give 6.5 g of the desiredproduct.

Preparation of [N-methyl-D-Pro]-Val-MeVal-Pro-Pro-NHBn×HCl

1.94 g (3 mmol) of D-Pro-Val-MeVal-Pro-Pro-NHBn×HCl was dissolved in 30ml methanol. To this solution was then added 0.3 g 10% Pd/charcoal and1.5 ml aqueous formaldehyde solution and the reaction mixture washydrogenated. Following filtration and evaporation of the solvents, theresulting residue was dissolved in water, adjusted to pH 2 and extractedtwice with diethyl ether and several additional times withdichloromethane. The aqueous phase was adjusted to pH 9-10 and extractedtwice with dichloromethane. The organic extracts were dried over sodiumsulfate and evaporated to dryness. The residue was crystallized as thehydrochloride salt to give 0.5 g of the desired product which wascharacterized by fast atom bombardment mass spectrometry ([M+H]+=625).

The compounds listed in Table 1 were prepared according to the methodsdescribed in Examples 1-4. Where compounds are referred to as “isomer 1”or “isomer 2”, isomer 1 is the diastereomer with the shorter retentiontime on the reversed phase analytical HPLC system. Fast atombombardment-mass spectrometry results for selected compounds areprovided in Table 2.

TABLE 1 Compound No. Compound 6 Xah Val Xaa Pro Xab 7 Xai Val Xaa ProXab 8 Xae Val Xaa Pro Xab 9 Xad Val Xaa Pro Xbr 10 Xam Val Xaa Pro Xab11 Xaw Ile Xaa Pro Xbx 12 Xao Val Xaa Pro Xab 13 Xad Val Xaa Pro Xap 14Xaq Val Xaa Pro Xab 15 Xar Val Xaa Pro Xab 16 Xas Val Xaa Pro Xab 17 XatVal Xaa Pro Xab isomer 1 18 Xat Val Xaa Pro Xab isomer 2 19 Xaf Val XaaPro Xab 20 Xav Val Xaa Pro Xab 21 Xag Val Xaa Pro Xab 22 Xax Val Xaa ProXab isomer 1 23 Xax Val Xaa Pro Xab isomer 2 24 Xay Val Xaa Pro Xab 25Xaz Val Xaa Pro Xab isomer 1 26 Xaz Val Xaa Pro Xab isomer 2 27 Xba ValXaa Pro Xab 28 Xbb Val Xaa Pro Xab 29 Xbc Val Xaa Pro Xab 30 Xbd Val XaaPro Xab isomer 1 31 Xbd Val Xaa Pro Xab isomer 2 32 Xbe Val Xaa Pro Xabisomer 1 33 Xbe Val Xaa Pro Xab isomer 2 34 Xbf Val Xaa Pro Xab isomer 135 Xbg Val Xaa Pro Xab 36 Xbh Val Xaa Pro Xab isomer 1 37 Xbh Val XaaPro Xab isomer 2 38 Xbi Val Xaa Pro Xab isomer 1 39 Xbi Val Xaa Pro Xabisomer 2 40 Xbk Val Xaa Pro Xab isomer 1 41 Xbk Val Xaa Pro Xab isomer 242 Xbl Val Xaa Pro Xab 43 Xbf Val Xaa Pro Xab isomer 2 44 Xbm Val XaaPro Xab 45 Xaw Val Xaa Pro Xbn 46 Xbo Val Xaa Pro Xbn isomer 1 47 XboVal Xaa Pro Xbn isomer 2 48 Xaw Val Xaa Pro Xbp 49 Xbo Val Xaa Pro Xbpisomer 1 50 Xbo Val Xaa Pro Xbp isomer 2 51 Xaw Val Xaa Pro Xbq 52 XawVal Xaa Pro Xbr 53 Xbs Val Xaa Pro Xbt isomer 1 54 Xbl Val Xaa Pro Xabisomer 1 55 Xbl Val Xaa Pro Xab isomer 2 56 Xbu Val Xaa Pro Xab isomer 157 Xbv Val Xaa Pro Xab 58 Xbw Val Xaa Pro Xab isomer 1 59 Xbw Val XaaPro Xab isomer 2 60 Xbs Val Xaa Pro Xbt isomer 2 61 Xbu Val Xaa Pro Xabisomer 2 62 Xbo Val Xaa Pro Xbr isomer 1 63 Xbo Val Xaa Pro Xbr isomer 264 Xbo Val Xaa Pro Xbq isomer 1 65 Xbo Val Xaa Pro Xbq isomer 2 66 XawVal Xaa Pro Xbx 67 Xby Val Xaa Pro Xab 68 Xbz Val Xaa Pro Xab 69 Xca ValXaa Pro Xab isomer 1 70 Xca Val Xaa Pro Xab isomer 2 71 Xbo Val Xaa ProXbx isomer 1 72 Xbo Val Xaa Pro Xbx isomer 2 73 Xau Val Xaa Pro Xbp 74Xau Val Xaa Pro Xbx 75 Xbi Val Xaa Pro Xbx isomer 2 76 Xau Val Xaa ProXab isomer 1 77 Xau Val Xaa Pro Xab isomer 2 78 Xau Val Xaa Pro Xcb 79Xbi Val Xaa Pro Xcb isomer 1 80 Xbi Val Xaa Pro Xcb isomer 2 81 Xbi ValXaa Pro Xcc isomer 1 82 Xbi Val Xaa Pro Xcc isomer 2 83 Xbi Val Xaa ProXcd 84 Xbk Val Xaa Pro Xcc isomer 1 85 Xbk Val Xaa Pro Xcc isomer 2 86Xax Val Xaa Pro Xbp isomer 1 87 Xax Val Xaa Pro Xbp isomer 2 88 Xbk ValXaa Pro Xcb isomer 1 89 Xbk Val Xaa Pro Xcb isomer 2 90 Xau Val Xaa ProXcc 91 Xau Val Xaa Pro Xcd 92 Xba Val Xaa Pro Xcb isomer 1 93 Xba ValXaa Pro Xcb isomer 2 94 Xbo Val Xaa Pro Xbp isomer 1 95 Xbo Val Xaa ProXbp isomer 2 96 Xau Val Xaa Pro Xbp isomer 1 97 Xau Val Xaa Pro Xbpisomer 2 98 Xbi Val Xaa Pro Xcd isomer 2 99 Xbk Val Xaa Pro Xcd 100 XbaVal Xaa Pro Xbp isomer 1 101 Xba Val Xaa Pro Xbp isomer 2 102 Xba ValXaa Pro Xcc isomer 1 103 Xba Val Xaa Pro Xcc isomer 2 104 Xba Val XaaPro Xcd 105 Xce Val Xaa Pro Xab 106 Xcf Val Xaa Pro Xab 107 Xcg Val XaaPro Xab isomer 1 108 Xcg Val Xaa Pro Xab isomer 2 109 Xaw Val Xaa ProXch 110 Xaw Val Xaa Pro Xci 111 Xaw Val Xaa Pro Xck 112 Xaw Val Xaa ProXcl 113 Xaw Val Xaa Pro Xcm 114 Xaw Val Xaa Pro Xcn 115 Xaw Val Xaa ProXco 116 Xaw Val Xaa Pro Xcp 117 Xaw Val Xaa Pro Xcq 118 Xaw Val Xaa ProXcr 119 Xad Val Xaa Pro Xch 120 Xad Val Xaa Pro Xci 121 Xad Val Xaa ProXck 122 Xad Val Xaa Pro Xcl 123 Xad Val Xaa Pro Xcm 124 Xad Val Xaa ProXcn 125 Xad Val Xaa Pro Xco 126 Xad Val Xaa Pro Xcp 127 Xad Val Xaa ProXcq 128 Xad Val Xaa Pro Xcr 129 Xad Val Xaa Pro Xbx 130 Xau Val Xaa ProXch 131 Xau Val Xaa Pro Xci 132 Xau Val Xaa Pro Xck 133 Xau Val Xaa ProXcl 134 Xau Val Xaa Pro Xcm 135 Xau Val Xaa Pro Xcn 136 Xau Val Xaa ProXco 137 Xau Val Xaa Pro Xcp 138 Xau Val Xaa Pro Xcq 139 Xau Val Xaa ProXcr 140 Xau Val Xaa Pro Xbr 141 Xad Val Xaa Xal Xbx 142 Xau Val Xaa XalXbx 143 Xaw Val Xaa Xal Xbx 144 Xad Val Xaa Xal Xch 145 Xau Val Xaa XalXch 146 Xaw Val Xaa Xal Xch 147 Xad Val Xaa Xal Xcr 148 Xau Val Xaa XalXcr 149 Xaw Val Xaa Xal Xcr 150 Xad Val Xaa Xan Xbx 151 Xau Val Xaa XanXbx 152 Xaw Val Xaa Xan Xbx 153 Xad Val Xaa Xan Xch 154 Xau Val Xaa XanXch 155 Xaw Val Xaa Xan Xch 156 Xad Val Xaa Xan Xcr 157 Xau Val Xaa XanXcr 158 Xaw Val Xaa Xan Xcr 159 Xau Ile Xaa Pro Xbx 160 Xad Ile Xaa ProXbx 161 Xaw Ile Xaa Pro Xch 162 Xad Ile Xaa Pro Xch 163 Xau Ile Xaa ProXch 164 Xaw Xcs Xaa Pro Xch 165 Xad Xcs Xaa Pro Xch 166 Xau Xcs Xaa ProXch 167 Xaw Xcs Xaa Pro Xbx 168 Xad Xcs Xaa Pro Xbx 169 Xau Xcs Xaa ProXbx 170 Xaw Val Xct Pro Xch 171 Xad Val Xct Pro Xch 172 Xau Val Xct ProXch 173 Xaw Val Xct Pro Xbx 174 Xad Val Xct Pro Xbx 175 Xau Val Xct ProXbx

The symbols Xaa in Table 1 represent the following amino acids orresidues thereof:

-   Xaa: N-methyl-valine-   Xab: Prolyl N-benzylamide-   Xac: L-N-methyl-piperidine-2-carboxylic acid-   Xad: D-N-methyl-piperidine-2-carboxylic acid-   Xae: N-methyl-L-proline-   Xaf: N-methyl-L-thiazolidine-4-carboxylic acid-   Xag: N,N-dimethylglycine-   Xah: L-proline-   Xai: L-piperidine-2-carboxylic acid-   Xak: 2-[N,N-dimethylamino]-isobutyric acid-   Xal: L-thiazolidine-4-carboxylic acid-   Xam: N-propyl-D-piperidine-2-carboxylic acid-   Xan: L-3,4-didehydroproline-   Xao: D-piperidine-2-carboxylic acid-   Xap: proline tert.butylester-   Xaq: N-ethyl-D-piperidine-2-carboxylic acid-   Xar: N-methyl[2,2,5,5-tetramethyl]-L-thiazolidine-2-carboxylic acid-   Xas: N-isopropyl-D-piperidine-2-carboxylic acid-   Xat: N,N-dimethyl-2-cyclopropyl-glycine-   Xau: N,N-dimethyl-2-ethyl-2-phenyl-glycine-   Xav: D-proline-   Xaw: N-methyl-D-proline-   Xax: N,N-dimethyl-2-[4-fluoro]phenyl-glycine-   Xay: 1-aza-[3,3,0]bicyclooctyl-5-carboxylic acid-   Xaz: N,N-dimethyl-2-[4-fluoro]phenyl-glycine-   Xba: N-methyl-[2,2,5,5-tetramethyl]-thiazolidine-2-carboxylic acid-   Xbb: 2-(R,S)-ethyl-2-phenyl-glycine-   Xbc: D,L-1-aminoindane-1-carboxylic acid-   Xbd: N,N-dimethyl-2-(R,S)-methyl-2-phenyl-glycine-   Xbe: 2-[N,N-dimethylamino]indane-2-carboxylic acid-   Xbf:    5-[N,N-dimethylamino]-5,6,7,8-tetrahydro-naphthalene-5-carboxylic    acid-   Xbg: N-isopropyl-2-(R,S)-ethyl-2-phenyl-glycine-   Xbh: 1-[N,N-dimethylamino]indane-2-carboxylic acid-   Xbi: N,N-dimethyl-2-propyl-2-phenyl-glycine-   Xbk: N,N-dimethyl-2-[4-methoxy]phenyl-glycine-   Xbl: N-methyl-3-hydroxy-D,L-valine-   Xbm: N,N-dimethyl-D,L-2-isopropyl-2-phenyl-glycine-   Xbn: proline-N-methoxy-N-methyl-amide-   Xbo: N-methyl-piperidine-2-carboxylic acid-   Xbp: proline-isopropylamide-   Xbq: proline-isoxazolidinyl-   Xbr: proline-N-methoxy-N-benzylamide-   Xbs: N-methyl-D,L-proline-   Xbt: proline-[5-phenyl]isoxazolidinyl-   Xbu: N-methyl-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid-   Xbv: N-methyl-azetidine-2-carboxylic acid-   Xbw: N-isopropyl-azetidine-2-carboxylic acid-   Xbx: proline-tert-butylamide-   Xby: N,N-dimethyl-[O-methyl]serine-   Xbz: N,N-dimethyl-[O-methyl]threonine-   Xca: N-methyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid-   Xcb: proline-pentyl(3)amide-   Xcc: proline-(R)-phenethylamide-   Xcd: proline-(S)-phenethylamide-   Xce: 1-[N,N-dimethylamino]cyclohexyl-1-carboxylic acid-   Xcf: 1-[N,N-dimethylamino]cyclopentyl-1-carboxylic acid-   Xcg: 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid-   Xch:

-   Xci:

-   Xck:

-   Xci:

-   Xcm:

-   Xcn:

-   Xco:

-   Xcp:

-   Xcq:

-   Xcr:

-   Xcs: L-2-tert-butyl-glycine-   Xct: N-methyl-L-Isoleucine

TABLE 2 Results of FAB-MS analysis of selected compounds Compound No.Mol. weight measured 1 639 2 639 3 627 4 703 5 625 6 611 7 625 8 625 10667 12 625 13 606 14 653 15 699 16 667 17 639 18 639 19 643 20 611 21599 22 693 23 693 24 651 25 693 26 693 27 699 28 675 29 673 30 689 31689 32 701 33 701 34 715 35 717 36 701 37 701 38 717 39 717 40 705 41705 42 643 43 715 44 703 45 579 46 593 47 593 48 577 49 591 50 591 51591 52 655 53 667 54 657 55 657 56 687 57 611 58 639 59 639 60 667 61687 62 669 63 669 64 605 65 605 66 591 67 643 68 657 69 687 70 687 71605 72 605 73 655 74 669 75 683 76 703 77 703 78 683 79 697 80 697 81731 82 731 83 731 84 719 85 719 86 645 87 645 88 685 89 685 90 717 91717 92 679 93 679 94 591 95 591 96 655 97 655 98 731 99 719 100 651 101651 102 713 103 713 104 713 105 666 106 653 107 687 108 687

Example 5 Evaluation of Biological Activity

In Vitro Methodology

Cytotoxicity was measured using a standard methodology for adherent celllines, such as the microculture tetrazolium assay (MTT). Details of thisassay have been published (Alley, M. C. et al., Cancer Research 48:589-601, (1988)). Exponentially growing cultures of HT-29 coloncarcinoma cells were used to make microtiter plate cultures. Cells wereseeded at 5000-20,000 cells per well in 96-well plates (in 150 mL ofmedia), and grown overnight at 37° C. Test compounds were added, in10-fold dilutions varying from 10⁻⁴ M to 10⁻¹⁰ M. Cells were thenincubated for 48 hours. To determine the number of viable cells in eachwell, the MTT dye was added (50 mL of a 3 mg/mL solution of3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide in saline).This mixture was incubated at 37° C. for 5 hours, and then 50 mL of 25%SDS, pH 2, was added to each well. After an overnight incubation, theabsorbance of each well at 550 mu was read using an ELISA reader. Thevalues for the mean+/−SD of data from replicated wells were calculated,using the formula % T/C (% viable cells treated/control). Theconcentration of test compound which gives a TIC of 50% growthinhibition was designated as the IC₅₀.

Table 3 presents the IC₅₀ values determined in the HT-29 assay for aseries of compounds of the invention.

TABLE 3 Compound No. HT-29 [IC₅₀] 1 4.7 × 10⁻⁸ 2 6.8 × 10⁻¹⁰ 3 3.5 ×10⁻⁸ 4 1.2 × 10⁻⁹ 5 5.0 × 10⁻⁹ 8 5.1 × 10⁻⁷ 10 1.3 × 10⁻⁷ 12 3.7 × 10⁻⁷13 1.0 × 10⁻⁹ 14 1.5 × 10⁻⁹ 15 1.7 × 10⁻⁷ 16 7.3 × 10⁻¹⁰ 17 6.3 × 10⁻⁸18 8.8 × 10⁻⁹ 22 6.4 × 10⁻⁷ 24 2.8 × 10⁻⁸ 27 3.7 × 10⁻⁸ 28 4.9 × 10⁻⁸ 293.6 × 10⁻⁸ 30 6.1 × 10⁻⁹ 31 2.0 × 10⁻⁷ 32 8.5 × 10⁻⁷ 33 1.2 × 10⁻⁶ 345.0 × 10⁻⁹ 35 1.4 × 10⁻⁷ 36 6.2 × 10⁻⁹ 37 1.9 × 10⁻⁷ 38 7.3 × 10⁻⁷ 392.5 × 10⁻⁸ 40 5.6 × 10⁻⁷ 41 7.3 × 10⁻⁶ 42 3.4 × 10⁻⁷ 43 5.9 × 10⁻⁸ 444.8 × 10⁻⁸ 45 5.6 × 10⁻⁸ 46 7.2 × 10⁻⁷ 47 2.3 × 10⁻⁸ 48 2.5 × 10⁻⁸ 498.8 × 10⁻⁸ 50 8.9 × 10⁻⁸ 51 4.6 × 10⁻⁸ 52 3.4 × 10⁻⁷ 53 5.0 × 10⁻⁹ 544.2 × 10⁻⁹ 55 5.6 × 10⁻⁸ 57 2.5 × 10⁻⁸ 58 6.3 × 10⁻⁸ 59 1.9 × 10⁻⁷ 601.8 × 10⁻⁹ 62 9.9 × 10⁻⁸ 63 5.6 × 10⁻⁸ 64 1.7 × 10⁻⁶ 65 9.7 × 10⁻⁸ 663.4 × 10⁻⁷ 67 3.4 × 10⁻⁷ 68 4.2 × 10⁻⁷ 70 7.1 × 10⁻⁶ 72 1.2 × 10⁻⁷ 731.4 × 10⁻⁹ 74 5.1 × 10⁻⁸ 75 8.5 × 10⁻⁷ 76 2.3 × 10⁻¹⁰ 77 7.2 × 10⁻⁹ 784.3 × 10⁻⁹ 79 1.7 × 10⁻⁶ 80 6.7 × 10⁻⁸ 81 1.3 × 10⁻⁷ 82 1.1 × 10⁻⁸ 831.3 × 10⁻⁷ 84 1.2 × 10⁻⁶ 85 9.5 × 10⁻⁶ 90 9.3 × 10⁻¹⁰ 91 8.3 × 10⁻¹⁰ 921.5 × 10⁻⁶ 93 1.8 × 10⁻⁶ 94 3.0 × 10⁻⁶ 95 1.1 × 10⁻⁸ 96 1.7 × 10⁻⁹ 973.2 × 10⁻⁸ 98 6.0 × 10⁻⁹ 99 3.8 × 10⁻⁶ 100 2.3 × 10⁻⁶ 101 2.1 × 10⁻⁶ 1021.2 × 10⁻⁷ 103 1.1 × 10⁻⁷ 104 3.5 × 10⁻⁶ 105 1.8 × 10⁻⁸ 106 9.7 × 10⁻⁸108 7.1 × 10⁻⁶In Vivo Methodology

Compounds of this invention may be further tested in any of the variouspreclinical assays for in vivo activity which are indicative of clinicalutility. Such assays are conducted with nude mice into which tumortissue, preferably of human origin, has been transplanted(“xenografted”), as is well known in this field. Test compounds areevaluated for their anti-tumor efficacy following administration to thexenograft-bearing mice.

More specifically, human tumors grown in athymic nude mice can betransplanted into new recipient animals, using tumor fragments which areabout 50 mg in size. The day of transplantation is designated as day 0.Six to ten days later, the mice are treated with the test compoundsgiven as an intravenous or intraperitoneal injection, in groups of 5-10mice at each dose. Compounds are given daily for 5 days, 10 days or 15days, at doses from 10-100 mg/kg body weight. Tumor diameters and bodyweights are measured twice weekly. Tumor masses are calculated using thediameters measured with Vernier calipers, and the formula:(length×width²)/2=mg of tumor weightMean tumor weights are then calculated for each treatment group, and T/Cvalues are determined for each group relative to the untreated controltumors.

Those skilled in the art will recognize or be able to ascertain using nomore than routine experimentation many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed in the scope of the following claims.

1. A compound of the formulaA-B-D-E-F-(G)_(r)-(K)_(s)-L wherein r and s are 0; A is an α-amino acidderivative of Formula III_(a),

wherein R_(a) is hydrogen or unsubstituted C₁-C₃-alkyl; R¹ _(a) isC₁-C₃-alkyl; R⁶ _(a) is methyl, hydroxyl- or methoxy-substitutedC₁-C₃-alkyl, phenyl, or fluorine- or methoxy-substituted phenyl; and R⁷_(a) is hydrogen or C₁-C₃-alkyl; B is valyl, isoleucyl, or2-tert-butylglycyl; D is N-methylvalyl or N-methylisoleucyl; E isprolyl, thiazolidinyl-4-carbonyl or 3,4-didehydroprolyl; F is prolyl;and L is N-benzylamide, N-methoxy-N-benzylamide, tert-butylamide,tert-butyl ester, N-methoxy-N-methylamide, isopropylamide, 5-phenylisoxasolidinyl, isoxazolidinyl, pentylamide, (R) or (S) phenethylamide,—O-tert-butyl, isoxazolidinyl, 5-phenyl isoxazolidinyl,

or a pharmaceutically acceptable salt thereof.
 2. A compound of claim 1selected from the group consisting of: Me₂Aib-Val-MeVal-Pro-Pro-NHBn[N,N-dimethyl-2-ethyl-2-phenylglycyl]-Val-MeVal-Pro-Pro-NHBn Xax Val XaaPro Xab isomer 1 Xax Val Xaa Pro Xab isomer 2 Xaz Val Xaa Pro Xab isomer1 Xaz Val Xaa Pro Xab isomer 2 Xbb Val Xaa Pro Xab Xbd Val Xaa Pro Xabisomer 1 Xbd Val Xaa Pro Xab isomer 2 Xbg Val Xaa Pro Xab Xbi Val XaaPro Xab isomer 1 Xbi Val Xaa Pro Xab isomer 2 Xbk Val Xaa Pro Xab isomer1 Xbk Val Xaa Pro Xab isomer 2 Xbl Val Xaa Pro Xab Xbm Val Xaa Pro XabXbl Val Xaa Pro Xab isomer 1 Xbl Val Xaa Pro Xab isomer 2 Xau Val XaaPro Xbp Xau Val Xaa Pro Xbx Xbi Val Xaa Pro Xbx isomer 2 Xau Val Xaa ProXab isomer 1 Xau Val Xaa Pro Xab isomer 2 Xau Val Xaa Pro Xcb Xbi ValXaa Pro Xcb isomer 1 Xbi Val Xaa Pro Xcb isomer 2 Xbi Val Xaa Pro Xccisomer 1 Xbi Val Xaa Pro Xcc isomer 2 Xbi Val Xaa Pro Xcd Xbk Val XaaPro Xcc isomer 1 Xbk Val Xaa Pro Xcc isomer 2 Xax Val Xaa Pro Xbp isomer1 Xax Val Xaa Pro Xbp isomer 2 Xbk Val Xaa Pro Xcb isomer 1 Xbk Val XaaPro Xcb isomer 2 Xau Val Xaa Pro Xcc Xau Val Xaa Pro Xcd Xau Val Xaa ProXbp isomer 1 Xau Val Xaa Pro Xbp isomer 2 Xbk Val Xaa Pro Xcd Xau ValXaa Pro Xch Xau Val Xaa Pro XCi Xau Val Xaa Pro Xck Xau Val Xaa Pro XclXau Val Xaa Pro Xcm Xau Val Xaa Pro Xcn Xau Val Xaa Pro Xco Xau Val XaaPro Xcp Xau Val Xaa Pro Xcq Xau Val Xaa Pro Xcr Xau Val Xaa Pro Xbr XadVal Xaa Xal Xbx Xau Val Xaa Xal Xbx Xaw Val Xaa Xal Xbx Xad Val Xaa XalXch Xau Val Xaa Xal Xch Xau Val Xaa Xal Xcr Xau Val Xaa Xan Xbx Xau ValXaa Xan Xch Xau Val Xaa Xan Xer Xau Ile Xaa Pro Xbx Xau Ile Xaa Pro XchXau Xcs Xaa Pro Xch Xau Xcs Xaa Pro Xbx Xau Val Xct Pro Xch and Xau ValXct Pro Xbx; or a pharmaceutically acceptable salt thereof, wherein: Xaais N-methyl-valine, Xab is Prolyl N-benzylamide, Xau isN,N-dimethyl-2-ethyl-2-phenyl-glycine, Xax is N,Ndimethyl-2-[2-fluoro]phenyl-glycine, Xaz isN,N-dimethyl-2-[4-fluoro]phenyl-glycine, Xbb is2-(R,S)-ethyl-2-phenyl-glycine, Xbd isN,N-dimethyl-2-(R,S)-methyl-2-phenyl-glycine, Xbg isN-isopropyl-2-(R,S)-ethyl-2-phenyl-glycine,Xbi isN,N-dimethyl-2-propyl-2-phenyl-glycine, Xbk isN,N-dimethyl-2-[4-methoxy]phenyl-glycine, Xbl isN-methyl-3-hydroxy-D,L-valine, Xbm isN,N-dimethyl-D,L-2-isopropyl-2-phenyl-glycine, Xbp isproline-isopropylamide, Xbr is proline-N-methoxy-N-benzylamide, Xbx isproline-tert-butylamide, Xcb is proline-pentyl(3)amide, Xcc isproline-(R)-phenethylamide, Xcd is proline-(S)-phenethylamide, Xch is

Xci is

Xck is

Xcl is

Xcm is

Xcn is

Xco is

Xcp is

Xcq is

Xcr

and Xct is N-methyl-L-isoleucine.
 3. The compound of claim 2, having thestructure: Me₂Aib-Val-MeVal-Pro-Pro-NHBn or[N,N-dimethyl-2-ethyl-2-phenylglycyl]-Val-MeVal-Pro-Pro-NHBn or apharmaceutically acceptable salt thereof.
 4. The compound of claim 2,having the structure: Xax Val Xaa Pro Xab isomer 1 Xax Val Xaa Pro Xabisomer 2 Xaz Val Xaa Pro Xab isomer 1 Xaz Val Xaa Pro Xab isomer 2 XbbVal Xaa Pro Xab Xbd Val Xaa Pro Xab isomer 1 or Xbd Val Xaa Pro Xabisomer 2; or a pharmaceutically acceptable salt thereof.
 5. The compoundof claim 2, having the structure: Xbg Val Xaa Pro Xab Xbi Val Xaa ProXab isomer 1 Xbi Val Xaa Pro Xab isomer 2 Xbk Val Xaa Pro Xab isomer 1or Xbk Val Xaa Pro Xab isomer 2; or a pharmaceutically acceptable saltthereof.
 6. The compound of claim 2, having the structure: Xbl Val XaaPro Xab or Xbm Val Xaa Pro Xab or a pharmaceutically acceptable saltthereof.
 7. The compound of claim 2, having the structure: Xbl Val XaaPro Xab isomer 1 or Xbl Val Xaa Pro Xab isomer 2 or a pharmaceuticallyacceptable salt thereof.
 8. The compound of claim 2, having thestructure: Xau Val Xaa Pro Xbp Xau Val Xaa Pro Xbx Xbi Val Xaa Pro Xbxisomer 2 Xau Val Xaa Pro Xab isomer 1 Xau Val Xaa Pro Xab isomer 2 XauVal Xaa Pro Xcb Xbi Val Xaa Pro Xcb isomer 1 Xbi Val Xaa Pro Xcb isomer2 Xbi Val Xaa Pro Xcc isomer 1 or Xbi Val Xaa Pro Xcc isomer 2; or apharmaceutically acceptable salt thereof.
 9. The compound of claim 2,having the structure: Xbi Val Xaa Pro Xcd Xbk Val Xaa Pro Xcc isomer 1Xbk Val Xaa Pro Xcc isomer 2 Xax Val Xaa Pro Xbp isomer 1 Xax Val XaaPro Xbp isomer 2 Xbk Val Xaa Pro Xcb isomer 1 Xbk Val Xaa Pro Xcb isomer2 Xau Val Xaa Pro Xcc or Xau Vat Xaa Pro Xcd or a pharmaceuticallyacceptable salt thereof.
 10. The compound of claim 2, having thestructure: Xau Val Xaa Pro Xbp isomer 1 Xau Val Xaa Pro Xbp isomer 2 orXbk Val Xaa Pro Xcd or a pharmaceutically acceptable salt thereof. 11.The compound of claim 2, having the structure: Xau Val Xaa Pro Xch XauVal Xaa Pro Xci Xau Val Xaa Pro Xck or Xau Val Xaa Pro Xcl; or apharmaceutically acceptable salt thereof.
 12. The compound of claim 2,having the structure: Xau Val Xaa Pro Xcm Xau Val Xaa Pro Xcn Xau ValXaa Pro Xco Xau Val Xaa Pro Xcp Xau Val Xaa Pro Xcq Xau Val Xaa Pro XcrXau Val Xaa Pro Xbr or Xau Val Xaa Xal Xbx or a pharmaceuticallyacceptable salt thereof.
 13. The compound of claim 2, having thestructure: Xau Val Xaa Xal Xch Xau Val Xaa Xal Xcr or Xau Val Xaa XanXbx or a pharmaceutically acceptable salt thereof.
 14. The compound ofclaim 2, having the structure: Xau Val Xaa Xan Xch Xau Val Xaa Xan XcrXau Xaa Pro Xbx or Xau Ile Xaa Pro Xch; or a pharmaceutically acceptablesalt thereof.
 15. The compound of claim 2, having the structure: Xau XcsXaa Pro Xch or Xau Xcs Xaa Pro Xbx; or a pharmaceutically acceptablesalt thereof.
 16. The compound of claim 2, having the structure: Xau ValXct Pro Xch or Xau Val Xct Pro Xbx; or a pharmaceutically acceptablesalt thereof.